Re: [PATCH 2/4] iomap: iomap_dio_rw() handles all sync writes

[Jan Kara <jack@suse.cz>]

On Wed 18-04-18 14:08:26, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> Currently iomap_dio_rw() only handles (data)sync write completions
> for AIO. This means we can't optimised non-AIO IO to minimise device
> flushes as we can't tell the caller whether a flush is required or
> not.
> 
> To solve this problem and enable further optimisations, make
> iomap_dio_rw responsible for data sync behaviour for all IO, not
> just AIO.
> 
> In doing so, the sync operation is now accounted as part of the DIO
> IO by inode_dio_end(), hence post-IO data stability updates will no
> long race against operations that serialise via inode_dio_wait()
> such as truncate or hole punch.
> 
> Signed-Off-By: Dave Chinner <dchinner@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/iomap.c        | 22 +++++++++++++++-------
>  fs/xfs/xfs_file.c |  5 -----
>  2 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/iomap.c b/fs/iomap.c
> index afd163586aa0..1f59c2d9ade6 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -685,6 +685,7 @@ EXPORT_SYMBOL_GPL(iomap_seek_data);
>   * Private flags for iomap_dio, must not overlap with the public ones in
>   * iomap.h:
>   */
> +#define IOMAP_DIO_NEED_SYNC	(1 << 29)
>  #define IOMAP_DIO_WRITE		(1 << 30)
>  #define IOMAP_DIO_DIRTY		(1 << 31)
>  
> @@ -759,6 +760,13 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  			dio_warn_stale_pagecache(iocb->ki_filp);
>  	}
>  
> +	/*
> +	 * If this is a DSYNC write, make sure we push it to stable storage now
> +	 * that we've written data.
> +	 */
> +	if (ret > 0 && (dio->flags & IOMAP_DIO_NEED_SYNC))
> +		ret = generic_write_sync(iocb, ret);
> +
>  	inode_dio_end(file_inode(iocb->ki_filp));
>  	kfree(dio);
>  
> @@ -768,14 +776,8 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>  static void iomap_dio_complete_work(struct work_struct *work)
>  {
>  	struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work);
> -	struct kiocb *iocb = dio->iocb;
> -	bool is_write = (dio->flags & IOMAP_DIO_WRITE);
> -	ssize_t ret;
>  
> -	ret = iomap_dio_complete(dio);
> -	if (is_write && ret > 0)
> -		ret = generic_write_sync(iocb, ret);
> -	iocb->ki_complete(iocb, ret, 0);
> +	dio->iocb->ki_complete(dio->iocb, iomap_dio_complete(dio), 0);
>  }
>  
>  /*
> @@ -961,6 +963,10 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
>  	return copied;
>  }
>  
> +/*
> + * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO
> + * is being issued as AIO or not.
> + */
>  ssize_t
>  iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  		const struct iomap_ops *ops, iomap_dio_end_io_t end_io)
> @@ -1006,6 +1012,8 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  			dio->flags |= IOMAP_DIO_DIRTY;
>  	} else {
>  		dio->flags |= IOMAP_DIO_WRITE;
> +		if (iocb->ki_flags & IOCB_DSYNC)
> +			dio->flags |= IOMAP_DIO_NEED_SYNC;
>  		flags |= IOMAP_WRITE;
>  	}
>  
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 6f15027661b6..0c4b8313d544 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -570,11 +570,6 @@ xfs_file_dio_aio_write(
>  	 * complete fully or fail.
>  	 */
>  	ASSERT(ret < 0 || ret == count);
> -
> -	if (ret > 0) {
> -		/* Handle various SYNC-type writes */
> -		ret = generic_write_sync(iocb, ret);
> -	}
>  	return ret;
>  }
>  
> -- 
> 2.16.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR